Different chemical reactions are used in combinations in chemical synthesis in order to get a desired product. In biochemistry, series of chemical reactions catalyzed by enzymes form metabolic pathways, by which syntheses and decompositions ordinarily impossible in conditions within a cell are performed.

Reaction types

The large diversity of chemical reactions and approaches to their study results in the existence of several concurring, often overlapping, ways of classifying them. Below are examples of widely used terms for describing common kinds of reactions.

• Isomerisation, in which a chemical compound undergoes a structural rearrangement without any change in its net atomic composition; see stereoisomerism
• Direct combination or synthesis, in which 2 or more chemical elements or compounds unite to form a more complex product:

  N₂ + 3 H₂ → 2 NH₃

  2 H₂O → 2 H₂ + O₂

  2 Na(s) + 2 HCl(aq) → 2 NaCl(aq) + H₂(g)

  NaCl(aq) + AgNO₃(aq) → NaNO₃(aq) + AgCl(s)

  • Arrhenius definition: Acids dissociate in water releasing H₃O⁺ ions; bases dissociate in water releasing OH^- ions.
  • Brønsted-Lowry definition: Acids are proton (H⁺) donors; bases are proton acceptors. Includes the Arrhenius definition.
  • Lewis definition: Acids are electron-pair acceptors; bases are electron-pair donors. Includes the Brønsted-Lowry definition.

  2 S₂O₃²⁻(aq) + I₂(aq) → S₄O₆²⁻(aq) + 2 I⁻(aq)

  In which I₂ is reduced to I^- and S₂O₃^2- (thiosulfate anion) is oxidized to S₄O₆^2-.

  • Combustion, a kind of redox reaction in which any combustible substance combines with an oxidizing element, usually oxygen, to generate heat and form oxidized products. The term combustion is usually used for only large-scale oxidation of whole molecules, i.e. a controlled oxidation of a single functional group is not combustion.

    C₁₀H₈+ 12 O₂ → 10 CO₂ + 4 H₂O

    CH₂S + 6 F₂ → CF₄ + 2 HF + SF₆

    Organic reactions encompass a wide assortment of reactions involving compounds which have carbon as the main element in their molecular structure. The reactions in which an organic compound may take part are largely defined by its functional groups. Defined in opposition to inorganic reactions. Reactions can also be classified according to their mechanism, some typical examples being:

    • Reactions of ions, e.g. disproportionation of hypochlorite
    • Reactions with reactive ionic intermediates, e.g. reactions of enolates
    • Radical reactions, e.g. combustion at high temperature
    • Reactions of carbenes